That's NOT how the Cowboys (and many other teams) play Cover 4. In the Cowboys' Cover 4, the safeties' primary responsibility is man-to-man coverage on the inside receiver if he runs a vertical route. The cornerbacks play man-to-man on the outside receivers. If the inside receiver does not run a vertical route, the safety can then help on the outside receiver.
On the first play, Roy's man (Cooley) ran a vertical route (a post), so Roy had NO coverage responsibility on Moss. He reacted to the ball being thrown and almost made the play anyway, but that was in no way, shape or form his responsibility. On Moss' second TD, Roy's man (Cooley) started to run a vertical route but cut it to a deep out. Even though Roy diagnosed the play early, by the time Cooley started to make his cut, it was too late for Roy to cover Moss. In that scheme against that play, the only way Roy could have been responsible for that touchdown is if he had ignored his primary responsibility on the play. That's why when Parcells was asked point-blank if Roy was responsible for Moss' TD catches, he said no, those really weren't his plays.